The removal of sulfur from hydrocarbon feedstreams is an important separation in the oil, gas and chemical process industries. Typical hydrocarbon processing often includes at least one processing step which is sensitive to sulfur present in the feedstream. For example, in hydrocarbon conversion processes where hydrocarbon feeds are catalytically converted to hydrocarbon products, the catalyst used in the conversion process may be sensitive to sulfur. That is, the presence of sulfur in the feedstream may deactivate or inhibit in some way the catalyst in the conversion process. Generally, the presence of such a sulfur-sensitive step will necessitate the removal of all or most of the sulfur prior to its being introduced into the sulfur-sensitive step.
Further, there are many products in these industries in which sulfur must be removed to conform to a product specification. For example, transportation fuels may be limited to low levels of sulfur. In typical hydrocarbon conversion processes for forming sulfur-sensitive products, sulfur is removed by a hydrodesulfurization step. Such a hydrodesulfurization step generally involves passing a heated, vaporized feedstream to a hydrotreating reactor that catalytically converts the sulfur in the feedstream to hydrogen sulfide, passing the hydrotreating product to a condenser in which a portion of the gaseous hydrogen sulfide is condensed with the remainder of the hydrogen sulfide leaving as overhead, and passing the liquid product to a stripper wherein the condensed hydrogen sulfide in the liquid product is removed. In lieu of a stripper, a hydrogen sulfide adsorption bed may also be used to adsorb hydrogen sulfide from the liquid product.
Transportation fuels are also required to meet certain research octane numbers (RON). Retention of a sufficiently high octane number can be difficult when removing sulfur from hydrocarbon feedstocks holding substantial amounts of sulfur, as hydrodesulfurization processes cause losses in the processed hydrocarbon's octane number.
Accordingly, it is desirable to provide methods and apparatuses for desulfurizing hydrocarbon streams. Also, it is desirable to provide methods and apparatuses that perform a moderate hydrodesulfurization process on a portion of the hydrocarbon stream to retain its octane number while performing a deep hydrodesulfurization process on another portion of a hydrocarbon stream. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.